Screen cloth element

Abstract: Detachable screen cloths (14) are fixed on a screen cloth element (11) having a rigid support frame (12, 13) serving as a holder and intended to be fixed in the screen frame (10) of a screening machine. The detachable screen cloths (14) have a rigid screen cloth frame (30, 31) surrounded at least partially by elastomeric material. A laterally open guide device (32, 33) in the rigid mounting frame (12, 13) of the screen cloth element is designed for sliding engagement with the screen cloth (14) during the insertion thereof into the guide device and is also designed during screening to prevent relative movements between the screen cloth (14) and the rigid mounting frame (12, 13) of the screen cloth elements in directions making an angle with the plane of the screen cloth.

Description: The present invention relates to a screen cloth element of the type stated in the preamble of claim 1. A very common type of screening machine has a screen frame, in which a number of screen cloth elements are mounted after one another and most often in overlapping relationship to provide agitation of the screening material during the screening operation, while vibrating the screen cloth frame of the screening machine. Generally, the different screen cloth elements are designed with a rigid frame which serves to hold a screen cloth of elastomeric material, or other material, in a tensioned state. The rigid frame sometimes also has crossbars for additionally stiffening the screen cloth. The rigid frame and the optional crossbars are generally integrated in the screen cloth material and sometimes form projecting beams on the underside of the screen cloths. There are different methods for fixing the individual screen cloth elements. In early screen constructions, the screen cloth elements were applied on inwardly projecting flanges on the screen frame of the screening machine and were held depressed against these flanges by clamping bars, most often coated with wear- and abrasion resistant elastomeric material. Subsequently, it has become common practice to fix the screen cloth elements in the screen frame of the screening machine by means of different types of snap-lock means. Examples of this type of constructions are described e.g. in SE-B-422,418 (corresponding to US-A-4,141,821), US-A-4,960,510 and WO 84-02290 (corresponding to US-A-4,661,245). Another type of snap lock is suggested in DE-A-1,186,311. According to this document, the screen is formed of screen plates of a brittle ceramic material or any other wear-resistant rigid, brittle material. The screen plates are held in place by rubber strips which not only retain the rigid plates by yielding resiliently during mounting while the plates are depressed to their mounting positions, but also serve as elastic dampers to prevent the screen plates, consisting of brittle material, from cracking during the screening operation. When the plates are being depressed, they are pressed downwards almost perpendicularly to their planes, the rubber strips yielding resiliently to make room for the screen plates. This resilient mounting or damping also results in reduced wear, in that the plates yield when subjected to heavy impacts from the screening material. A further development of the concept of mounting the screen cloth elements by means of snap locks in the screen frame of the screening machine is shown and described in SE-B-460,340 (corresponding to EP-B-0,364,541 and US-A-5,085,324). In this prior-art screen, the different screen cloth elements are fixed to the screen frame of the screening machine by means of snap-lock means. One part of the snap-lock means is integrally formed with the screen cloth element and is disposed close to one end thereof. The other part of the snap-lock means consists of a thickened portion at the upper edge of a carrier element in the screen frame of the screening machine. The other end of the screen cloth element rests on a projecting abutment surface on the carrier element and is clamped between this abutment surface and a projecting edge portion of the preceding screen cloth element. This last-mentioned type of screen cloth elements and screens has been widely used, since worn screen cloth elements can easily be exchanged for new ones. Moreover, such an exchange can be restricted to those parts of the screening machine which are subjected to the greatest wear. It has however been found that it would be advantageous, from different aspects, if one could obtain yet greater flexibility in the design of the screen surface and yet greater freedom for exchanging worn screen cloth elements within particularly exposed screen surface portions in screening machines where the screen surface is formed of a number of succeeding screen cloth elements, optionally arranged in cascade manner relative to one another. One object of the present invention therefore is to meet these requirements. Another object of the invention is to enable an extended time of use for such screen cloth element portions as have not been completely worn down during the screening process, so that these portions can be used several times and only the worn portions of the screen cloth elements are exchanged. A special object of the invention is to further develop the advantageous screen design with overlapping screen cloth elements which is the subject matter of SE-B-460,340 and its counterparts EP-B-0,364,541 and US-A-5,085,324. These and other objects of the invention are achieved by means of screen cloth elements having the features recited in claim 1 Especially advantageous embodiments are defined in the subclaims. In the invention, use is thus made of detachable screen cloths which are fixed on a screen cloth element having a rigid mounting frame and intended to be fixed in the screen frame of a screening machine. The detachable screen cloths have a rigid screen cloth frame which preferably is at least partially surrounded by elastomeric material. A laterally open guide device in the rigid mounting frame of the screen cloth element is designed for sliding engagement with the screen cloth during the insertion thereof into the guide device and is further designed during screening to prevent relative movements between the screen cloth and the screen cloth elements in directions making an angle with the plane of the screen cloth. For mounting and dismounting the screen cloths, these are inserted laterally in or drawn laterally out of the remainder of the screen cloth elements like a drawer. By this design of the screen cloth elements and the screen cloths inserted therein, it becomes possible to quickly exchange precisely those portions of the total screen surface which have become worn, and to use the remaining parts for further screening. Moreover, a greater freedom of choice is obtained as regards the size of the screening apertures or screening gaps as well as the choice of material of the exchangeable screen cloths. The invention also makes it possible to optimise the choice of material for the different parts of the screen cloth elements, such that the rigid frame of the screen cloth elements, for example, is integrated in a wear- and abrasion-resistant rubber material having properties that are especially well suited for forming the mounting parts of the screen cloth elements, while a different material is selected for the exchangeable screen cloths, so that these are given optimum properties for the intended screening work. It is thus possible to choose a harder elastomeric material for the mounting parts of the screen cloth elements and a softer elastomeric material for the exchangeable screen cloths if a sticky material is to be screened. Besides, it is possible in the same type of mounting parts to use screen cloths of the wire screen type or perforated ceramic plates. The exchangeable screen cloths can thus be formed from a material having optimum properties for the screening operation, while the rest of the screen cloth element may be formed from a material having optimum properties for the mounting and the retention of the screen cloths. Another major advantage of the screen cloth elements according to the present invention is that the operator of a particular screening machine is offered a substantial amount of freedom for choosing the screening material in one and the same machine, since he may in a simple manner replace one screen cloth surface with another while maintaining the majority of the screen cloth elements of the screening machine intact. By using exchangeable screen cloths of different types, it is thus possible to screen all sorts of screening materials, from sticky materials to coarse and fine material. The design of the apertures in the screen cloths can therefore be varied irrespective of the remaining parts of the screen cloth elements, and the exchangeable screen cloths may be designed as wire screens or perforated screens. Since the invention is particularly advantageous for use in connection with screen cloth elements according to SE-B-460,340 and its counterparts EP-B-0,364,541 and US-A-5,085,324, the invention will be described hereinafter by way of an embodiment which is based on this advantageous type of screens. The invention is however usable for all types of screen cloth elements having a rigid frame and a screen cloth retained thereby, and intended to be fixed in the screen frame of a screening machine. The invention will be described in more detail hereinbelow with reference to accompanying drawings showing a currently preferred best embodiment of the invention. Fig. 1 is a longitudinal section of a part of a screen having screen cloth elements according to the present invention. Fig. 2 shows on a larger scale a detail of Fig. 1. Fig. 3 is a section taken along line III-III in Fig. 1. Fig. 4 shows part of a section taken along line IV-IV in Fig. 3. Fig. 5 is a perspective view of a screen cloth element seen obliquely from below. Fig. 6 shows from above a screen cloth element according to Fig. 1 during the mounting of a screen cloth by the insertion thereof in a guide device. Fig. 7 is a section taken along line III-III through the screen cloth in Fig. 1. Fig. 8 is a section taken along line III-III through the screen cloth element with a screen cloth according to Fig. 1 mounted thereon. Fig. 9 is a section taken along line III-III through the mounting part of the screen cloth element prior to the mounting of the screen cloth. Fig. 10 is a section, similar to Fig. 1, of an individual screen cloth element in a further embodiment according to the invention. Fig. 11 is a view, similar to Fig. 6, of the screen cloth element according to Fig. 10 during the insertion of a screen cloth into a guide device in the mounting part of the screen cloth element. Fig. 12 is a section, similar to Fig. 3, of the screen cloth element according to Fig. 10. Fig. 13 is a section taken along line XIII-XIII in Fig. 12. As appears from Fig. 1, the screening machine has a screen frame 10, in which a number of screen cloth elements 11 according to the invention are mounted after one another. The screen cloth elements 11 comprise a rigid mounting frame in the form of a mounting part 12 and a rigid reinforcing core 13 provided therein. The reinforcing core 13 is integrated in a wear- or abrasion-resistant elastomeric material which may consist of natural or synthetic rubber or plastic. An exchangeable screen cloth 14 is mounted in the mounting part 12 in a manner which will be described in more detail hereinafter. As appears from Fig. 1, the ends of the successively mounted screen cloth elements are overlapping, so that the downstream end, as seen in the screening direction (arrow 15), of one screen cloth element is positioned on top of the upstream end of the following screen cloth element. The underside of the mounting part 12 adjacent its downstream end has a projection 16 with an undercut groove 17. The components 16 and 17 form one part of snap-lock means for locking the screen cloth element to the screen frame. The other part of the snap-lock means consists of a thickened edge portion 18 on a carrier element 19 included in the screen frame. This carrier element has a projecting flange or abutment surface 20. The upstream end 21 of the following screen cloth element rests on this abutment surface. The relative dimensions of the carrier element, the snap-lock means and the screen cloth elements are such that the upstream end of the following screen cloth element is clamped between the abutment surface 20 and the projecting edge portion 22 of the preceding screen cloth element. By this design, it is possible to reduce the number of snap-lock means required for the same number of screen cloth elements in one screen while simultaneously achieving a stepped screening surface which turns the screening material and thus, improves the screening efficiency. The upstream end of the uppermost screen cloth element rests on an abutment surface 23 on the screen frame 10 and is depressed against this abutment surface by a clamping element 24. The clamping element 24 also retains a sliding surface 25, along which the material to be screened passes down to the screen cloth elements. In the manufacture of the mounting part 12 of the screen cloth element, the frame 13 is placed in a vulcanising mould, such that it will abut on supporting bosses in five places where the vulcanising mould has inwardly extending abutment surfaces forming recesses on the underside of the mounting part or holder 12 to be formed. Four of the recesses 28 are visible in Fig. 5 and are disposed on the inside of the longitudinal edge stiffening means of the holder. The fifth recess is a narrow groove 29 at the upstream end of the holder 12, this recess being illustrated in more detail in Figs 3 and 4. As mentioned above, a screen cloth element according to the invention comprises a holder part or mounting part 12 and a screen cloth 14 insertable therein. The screen cloth 14 of elastomeric material has a rigid screen cloth frame 30 which is integrated in the elastomeric material and extends completely around the screen cloth 14 and which may advantageously have one or more crossbars 31, since the screen cloth element and the screen cloth have a substantial length, as seen in the screening direction (arrow 15). The crossbars 31 serve to stiffen the screen cloth and reduce the tendency of the screen cloth surfaces to flutter when the screen cloth 10 is vibrating. In the use of the invention, the screen cloth 14 is thus formed as a separate element or unit. For mounting the screen cloth 14 in the mounting part 12 of the screen cloth element, the part 12 has been designed with a guide device 32, 33, which is laterally open relative to the screen cloth element. This guide device is designed for sliding engagement with the screen cloth 14 during the insertion thereof into the holder part 12 and is also designed to prevent relative movements between the screen cloth 14 and the holder part 12 of the screen cloth element in directions making an angle with the plane of the screen cloth, especially at right angles thereto. Since the screen cloths are inserted in the holder part transversely of the screening direction of the screening machine, the screen cloths will be prevented from moving along the guides, once the screen elements have been mounted in the screen frame of the screening machine. Thus, the screen frame prevents movements in the transverse direction. In the screen cloth element according to the invention, the rigid frame or holder part 12 advantageously comprises a rigid frame core 13 and a coating of elastomeric material partially surrounding the core. Advantageously, the guide device is designed in this coating, as shown in the drawings. The guides 32, 33 of the guide device are advantageously so located in the holder part 12 of the screen cloth element as to be protected against contact with the screening material. To this end, the guide 32 at the upstream end of the screen cloth element is so positioned that this guide 32 and a portion of the screen cloth 14 are concealed under and protected by the projecting portion 22 of the immediately preceding screen cloth element, as appears from Figs 1 and 2. At the downstream end of the screen cloth element, the guide 33 is protected by the screen cloth 14 being designed with a projecting portion 34 which is recessed in the holder part 12 and is flush with the upwardly facing surface of the projecting portion 22 of the holder part. The projecting portion 34 may either end just after the guide 33, as shown in the embodiment according to Fig. 1, or extend as far as the end of the projecting portion 22, as shown in the embodiment of Fig. 2. For mounting and dismounting the screen cloths 14, these are laterally inserted in the holder part 12 of the screen cloth elements, as indicated by arrows 35 in Fig. 6. The screen cloths 14 then slide along the guides 32, 33, the insertion and extraction of the screen cloths being facilitated by the position of the rigid frame 30 of the screen cloth in the elastomeric material close to the portion of the screen cloth elastomeric material forming the guide surface which the guides 32, 33 of the holder part 12 engage. As appears from Fig. 8, the rigid frame 30 of the screen cloth 14 is disposed straight above the rigid frame 13 of the holder or mounting part 12 to be supported thereby. By this arrangement, the separate, inserted screen cloth will not as easily be depressed or deflected by the screening material placed thereon. Figs 10-13 show another embodiment of a screen cloth element according to the present invention. In this case, the screen cloth is designed as a wire screen 40. The wire screen has a rigid frame element 30 of metal which extends completely around the screen. This screen element is substantially completely embedded in elastomeric material in the same way as in the case of the screen cloths 14 in the previously described embodiments of the invention. The difference with respect to these embodiments is that undercut grooves 41 are provided in the underside of the elastomeric material on the inside of the frame element 30. The grooves 41 are intended to cooperate with transverse carrier rods 42 of metal. These carrier rods in turn are interconnected by the wires 43 of the wire screen. As appears from Figs 10-13, the screen wires 43 are wound one turn about each carrier rod. At the ends of the wire screen, the screen wires extend up to the inside of the elastomeric material surrounding the frame element 30. If so desired, the free ends 44 of the screen wires 43 may extend into downwardly-facing recesses in the elastomeric material. As appears from Fig. 12, the carrier rods 42 will be confined in their undercut grooves 41, once the carrier rods with the screen wires 43 disposed thereon have snapped in place in the grooves 41 and the screen cloth has been laterally inserted in the holder part 12. If the screen cloth is a wire screen, the screen wire elements need not necessarily be designed as shown in Figs 10-13. Thus, the screen wires 43 may instead extend straight from end to end and rest on the carrier rods 42 and be welded thereto. Alternatively, the screen wires 43 may be fixed directly on the frame element 30 on the screen cloth. In such a case, the screen wires 43 may be pretensioned, if so desired. A considerable advantage of the screen cloth element according to the present invention thus is that the operator of the screening machine can easily exchange the screen cloths in case of excessive wear, or when it is desirable to switch from one type of screen cloth to another. As mentioned above, the invention confers major advantages, in that only a small part of the screen cloth element is replaced when renovating the screen surface of the screening machine, and in that the holder part 12 of the screen cloth element is reused as a holder for new screen cloths. Another advantage is that stock-keeping is facilitated by the small screen cloth dimensions as compared with the whole screen cloth elements. The reduced dimensions are also advantageous in terms of manufacture, transportation and storage. The exchangeability and the ease with which exchanges can be made are also major advantages, in that it is easy to switch between different types of screening operations in the screening machine, i.e. by a simple exchange it is possible to alter the mesh size or the quality of the material in the very screen cloth surface so as to achieve optimum conditions for a large variety of screening material grades.

Claims: A screen cloth element intended to be fixed in the screen frame (10) of a screening machine and having a rigid mounting frame (12, 13) and a screen cloth (14, 40) which is retained thereby and which has a rigid screen cloth frame (30, 31) and is designed as a separate element, characterised in that the rigid mounting frame (12, 13) of the screen cloth element has a guide device (32, 33) laterally open relative to the plane of the screen cloth element and to the screening direction of the screening machine, and that the guide device (32, 33) is designed for sliding engagement with the screen cloth (14, 40) during the insertion thereof in the guide device (32, 33) and is further designed to prevent relative movements between the screen cloth (14) and the rigid mounting frame (12, 13) of the screen cloth element in directions making an angle with the plane of the screen cloth. A screen cloth element as claimed in claim 1, characterised in that the rigid screen cloth frame (30, 31) is at least partially surrounded by elastomeric material. A screen cloth element as claimed in claim 1 or 2, in which the rigid mounting frame (12, 13) of the screen cloth element comprises a rigid frame core (13) and a coating of wear- and abrasion-resistant elastomeric material at least partially surrounding said frame core, characterised in that the guide device (32, 33) is designed in said coating. A screen cloth element as claimed in claim 1, 2 or 3, characterised in that the guides (32, 33) of the guide device are so positioned in the screen cloth element as to be protected against contact with the screening material. A screen cloth element as claimed in claim 4, which is intended to be mounted in such a manner in the screen frame (10) of the screening machine that the ends of screen cloth elements mounted after one another are overlapping in roof-tile manner, characterised in that the guides (32, 33) are protected by the screen cloth (14, 40) covering the guides and/or by an adjoining screen cloth element covering the guides with an overlapping portion (22). A screen cloth element as claimed in any one of claims 1-5, characterised in that at least those parts of the screen cloth (14, 40) that cover the guides (32, 33) are formed from an abrasion-resistant elastomeric material, especially wear-resistant rubber. A screen cloth element as claimed in any one of the preceding claims, characterised in that the screen cloth (14, 40) has its rigid frame (30, 31) so designed that parts thereof are located in screen cloth portions adjacent the guide devices (32, 33). A screen cloth element as claimed in any one of the preceding claims, characterised in that the screen cloth (14, 40) has portions of its rigid frame (30, 31) located opposite corresponding portions of the rigid frame core (13) of the rigid mounting frame (12, 13). A screen cloth element as claimed in any one of claims 2-8, characterised in that undercut recesses (41) are formed in the coating partially surrounding the frame core (13) for receiving the ends of carrier rods (42) included in a separate wire screen (40), and for retaining the wire screen in the screen cloth element (11).

Inventors: MALMBERG MATS ANDERS, MALMBERG, MATS ANDERS
Applicants: SVEDALA TRELLEX AKTIEBOLAG
Application year: 1994
Main classification: B07B1
IPC codes: B07B1, B01D33